Kinetics and Mechanisms of Carbonyl Substitution Reactions of Bis(η5-cyclopentadienyl) Dicarbonyl Compounds of the Titanium Triad Metals

Article abstract of DOI:10.1021/ja00275a031

Kinetic studies were performed for CO substitution reactions of (η⁵-ring)2M(CO)2, where (η⁵-ring)=Cp, Cp^*, or Ind and M=Ti, Zr, or Hf.Nucleophiles used for these reactions include PMe2Ph, PMePh2, PPh3, P(n-Bu)3, and CO.The reaction rates of the titanium compounds were first order in substrate and zero order in entering nucleophile at nucleophile concentrations which gave the limiting reaction rate.The results indicate a dissociative mechanism.Activation parameters for these reactions are also in agreement with a dissociative process.In contrast, reaction rates of the zirconium and hafnium compounds are first order in both substrate and entering nucleophile, indicating an associative mechanism.This mechanistic difference may be attributed to steric considerations caused by the smaller size of titanium.Equilibrium constants and rate constants indicate a strong preference of the Ti, Zr, and Hf metallocene compounds for CO over PR3.